Competition in the manufacturing industry is growing at an accelerated rate due to globalization trend. This global competition urges manufacturing organizations to review and improve their processes in order to enhance and maintain their competitive advantage. One of those initiatives is the implementation of the Six Sigma methodology to analyze and reduce variation hence improving the processes of manufacturing organizations. This paper presents a Discrete Event Simulation methodology to support a Six Sigma approach for manufacturing organizations. Several approaches to implement Six Sigma focus on improving time management and reducing cycle time. However, these efforts may fail in their effective and practical implementation to achieve the desired results. Following the proposed methodology, a Discrete Event Simulation model was built to assist decision makers in understanding the behavior of the current manufacturing process. This approach helps to systematically define, measure and analyze the current state process to test different scenarios to improve performance. The paper proposes a systematic approach which allows for constant refinement of a process until a state of perfection is achieved. It applies an action research strategy to develop and validate the proposed modelling methodology in a British manufacturing organization competing in global markets.